The present invention relates to room temperature vulcanizable silicone rubber compositions which exhibit improved adhesion upon curing. More particularly, the present invention relates to room temperature vulcanizable silicone rubber compositions comprising a polydiorganosiloxane wherein the silicon atom at each polymer chain end is terminated with at least two hydrolyzable groups, a non-chelate condensation catalyst, and a metal chelate adhesion promoter.
Prior to the present invention it was well known in the art that various metal salts of carboxylic acids, metal chelates, organic acids and organic bases could be used as condensation catalysts for room temperature vulcanizable silicone rubber compositions.
Evans, U.S. Pat. No. 3,622,529, discloses a composition stable under substantially anhydrous conditions and curable to the solid, elastic state in the presence of moisture which comprises a silanol chainstopped polydiorganosiloxane, an imidatosilane of the formula ##STR1## where R and R.sup.2 are each organic radicals of not more than 18 carbon atoms selected from hydrocarbyl, halohydrocarbyl, nitrohydrocarbyl and alkoxyhydrocarbyl; R.sup.1 is hydrogen or a radical selected from hydrocarbyl, halohydrocarbyl, and cyanoalkyl; R.sup.3 is hydrogen or an organic radical of not more than 18 carbon atoms selected from hydrocarbyl, halohydrocarbyl, nitrohydrocarbyl, alkoxyhydrocarbyl, dialkylamino, and ##STR2## wherein R.sup.4 is an organic radical selected from aliphatic hydrocarbyl, aliphatic halohydrocarbyl, aliphatic nitrohydrocarbyl and ##STR3## where R.sup.5 and R.sup.6 are each aliphatic hydrocarbyl, a is an integer from 2 to 4, inclusive, b is an integer from 0 to 2, inclusive, d is 0 or 1, and the sum of a, b and d is 4, and, optionally, a minor amount of carboxylic acid salt and/or chelate of a metal ranging from lead to manganese, inclusive, in the electromotive series of metals.
Smith et al., U.S. Pat. No. 3,708,467, discloses a composition stable under substantially anhydrous conditions and curable to the solid, elastic state which comprises a silanol chainstopped polydiorganosiloxane, a silane represented by the formula R.sub.m Si(OR.sup.1).sub.4-m where R and R.sup.1 are radicals having not more than about 8 carbon atoms selected from the group consisting or hydrocarbyl, halohydrocarbyl and cyano lower alkyl, and a catalyst system containing a first catalyst which is a salt, alkoxide, hydroxide or oxide of a metal ranging from lead to manganese in the electromotive series of metals and a second catalyst which is a titanium chelate.
The present invention is based on the surprising discovery that improved adhesion is obtained if a polydiorganosiloxane having the silicon atom at each polymer chain end terminated with at least two hydrolyzable groups is employed in combination with a non-chelate condensation catalyst and a metal chelate adhesion promoter.